KR100435450B1 - Control apparatus for liquid o2 pump - Google Patents

Abstract

The present invention relates to an automatic precooling control device for a liquid oxygen pump that is capable of automatically performing precooling of the liquid oxygen pump and boosting the liquid oxygen to a set pressure when pumping the liquid oxygen from the liquid oxygen tank and supplying the oxygen to the oxygen use plant. It is about.

Accordingly, the present invention provides a pump in / out valve provided at the inlet and outlet of the oxygen pump to control the flow rate flowing from the liquid oxygen tank and the flow rate discharged from the pump, and the liquid oxygen pump driving start signal is inputted. Is automatically supplied to the liquid oxygen pump to control the opening amount of the pump inlet / outlet valves to precool the liquid oxygen pump, and the temperature detectors respectively provided to detect the inlet and outlet temperatures of the liquid oxygen pump. A precooling completion determination unit for determining whether the precooling is completed according to a temperature difference calculated by receiving the temperature of the pump inlet and outlet sides detected by the temperature detector; and when the precooling is completed, pumping and discharging the liquid oxygen. And a pump starting part for starting the liquid oxygen pump.

Description

Automatic precooling control device for liquid oxygen pump {CONTROL APPARATUS FOR LIQUID O2 PUMP}

The present invention relates to an automatic precooling control device for a liquid oxygen pump, and more particularly, when the liquid oxygen is pumped from a liquid oxygen tank and supplied to an oxygen using plant, the precooling of the liquid oxygen pump and the step of boosting the liquid oxygen to a set pressure are performed. It relates to an automatic precooling control device for a liquid oxygen pump that can automatically perform this.

In general, an oxygen plant uses oxygen in the air to produce oxygen and nitrogen, but there are various methods of producing oxygen, but in an apparatus producing a large amount of gas, a separation method using a temperature difference is used. In the oxygen production method using the temperature boiling point difference, when the temperature of the air composed of 21% oxygen and 79% nitrogen continues to decrease, oxygen gas is separated when the air temperature reaches -183 ° C, and nitrogen at -195 ° C. The gas is separated to produce oxygen gas and nitrogen gas, respectively.

Oxygen gas thus produced is supplied to all steel mills to produce steel products. Especially, oxygen gas is an indispensable gas in steel mills. Therefore, if no oxygen is supplied from the oxygen plant, all steel mills will be shut down.In order to prepare for emergencies, liquid oxygen, liquid nitrogen, and liquid argon tanks are installed as reserves for emergency situations. In the event of an emergency, liquid oxygen is pumped to an oxygen plant to ensure normal operation. At this time, the equipment used to boost the pressure of the liquid oxygen in the liquid oxygen tank to the oxygen use plant is a liquid oxygen pump.

1 is a block diagram showing a schematic configuration of a drive control apparatus for such a conventional liquid oxygen pump. As shown in FIG. 1, the driving control apparatus of the conventional liquid oxygen pump boosts the liquid oxygen of the liquid oxygen tank 1 to the oxygen pressure pressure by using the liquid oxygen pump 2 and then moves to an evaporator (not shown). It is supplied, vaporized in an evaporator, and then fed to an oxygen plant. At this time, since the temperature of the liquid oxygen of the liquid oxygen tank 1 is -183 ° C, and the temperature of the liquid oxygen pump 2 is about 20 to 30 ° C, the operation of precooling the liquid oxygen pump 2 pumps the liquid oxygen. This must be done before the task can be performed. This is to prevent the pump from being destroyed due to the temperature difference with the pump as soon as the cryogenic liquid oxygen reaches the pump and the pump becomes impossible, or the inflow of the low temperature liquid into the pump.

At this time, in the conventional pre-cooling method of the liquid oxygen pump, the operator first descends to the site for pre-cooling the pump, opens a small amount of the pre-cooling inlet valve 6 of the liquid oxygen pump, and introduces the cryogenic liquid oxygen into the liquid oxygen pump 2 and the temperature. Down, the precooling outlet valve 7 is opened, and the vaporized oxygen gas is discharged to the atmosphere. At this time, since the liquid oxygen is vaporized and released into the atmosphere during the precooling of the pump 2, there is a problem that the waste of the liquid oxygen becomes large, resulting in a loss of money.

In addition, the operator must operate the precooling inlet valve 6 slowly because the liquid oxygen pump 2 should be gradually lowered to prevent the pump shaft and bearing cracks resulting from the rapid cooling of the pump to low temperatures. When a sudden operation of the valve is made in this step-up process, the rotor blade and the sealing device of the motor is destroyed. However, in the related art, since the valve operation is based on the operator's driving experience, precise operation is difficult, and thus there is a high risk of generating a pump shaft and bearing cracks.

On the other hand, in order to determine whether the preliminary precooling of the liquid oxygen pump is completed, when the oxygen coming out of the precooling outlet valve is a liquid instead of a gas, the preliminary time is judged to be the completion point of precooling, and the preliminary cooling is stopped, and the pump inlet valve 4 and the pump outlet The valve 5 is opened to pump liquid oxygen from the liquid oxygen tank 1, and the pressure is increased to a predetermined pressure to supply the evaporator. At this time, the discharge pressure control unit 10 detects the pressure of the liquid oxygen supplied to the evaporator through the pump outlet valve 5 with the discharge pressure detector 8 to maintain 25 kg / cm 2 as an example of the pressure required for the oxygen use plant. The opening degree of the discharge pressure regulating valve 9 is adjusted to be possible. However, even when such pre-cooling determination is dependent on the operator's visual confirmation, there is a problem that the mechanical failure of the motor if the operator is wrongly judged. In addition, this conventional precooling determination method is time-consuming and cumbersome because all operations are performed manually, visually judged, and subsequent actions are taken. Therefore, there is a delay in supplying oxygen gas and accordingly, an oxygen-using plant In this case, there is a problem that the output of the produced product is reduced.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems, and its object is to automatically perform precooling so as not to cause mechanical breakdown of the liquid oxygen pump in precooling the liquid oxygen pump, and accurately complete the precooling. It is an object of the present invention to provide an automatic precooling control device for a liquid oxygen pump.

It is another object of the present invention to monitor the discharge pressure of liquid oxygen so that the discharge pressure can be automatically raised gradually, thereby preventing the destruction of the bearing and sealing device due to the sudden rise in the discharge pressure of the pump. It is to provide a control device.

1 is a block diagram showing a schematic configuration of a drive control apparatus of a conventional liquid oxygen pump.

2 is a system block diagram showing the configuration of an automatic precooling control device for a liquid oxygen pump according to the present invention.

3 is a circuit diagram showing a detailed configuration of an automatic precooling control unit according to the present invention.

Figure 4 (a) is a pre-cooling valve operation signal graph according to the pump temperature in the present invention, Figure 4 (b) is a graph showing the pump temperature trend.

5 is a circuit diagram showing a detailed configuration of an automatic boosting controller according to the present invention.

6 is a graph showing a pump discharge pressure control state according to the present invention.

7 is a test graph for determining a boosting time for implementing the present invention.

Explanation of symbols on the main parts of the drawings

1: liquid oxygen tank 2: liquid oxygen pump

3: Pump driven motor 4: Pump inlet valve

5: Pump outlet valve 11, 12: Temperature detector

20: discharge pressure control part 30: precooling completion part

40: pump start part 50: automatic precooling control part

60: Automatic boost control unit.

Automatic precooling control device of the liquid oxygen pump according to the present invention to achieve the above object

Hereinafter, with reference to the accompanying drawings, the configuration and effect of the automatic precooling control device for a liquid oxygen pump according to a preferred embodiment of the present invention will be described in detail.

2 is a system block diagram showing the configuration of an automatic precooling control device for a liquid oxygen pump according to the present invention. As shown in FIG. 2, the automatic precooling control device for the liquid oxygen pump according to the present invention controls the opening amount of the pump inlet valve 4 when a precooling start signal is input so that liquid oxygen is sequentially supplied to the liquid oxygen pump. The automatic precooling control unit 50 to control, the precooling completion determination unit 30 for determining whether the precooling is completed according to the temperature difference between the inlet and the outlet sides of the liquid oxygen pump 2, and the liquid oxygen pump when it is determined that the precooling is completed. (2) detects the pressure of the liquid oxygen discharged from the pump outlet part which is driven by the driving of the pump 2, and increases the discharge pressure of the liquid oxygen step by step according to the detected oxygen pressure. It is provided with an automatic boosting control unit 60 for outputting a control signal to the discharge pressure adjusting unit 20.

In addition, in the present invention, temperature detectors 11 and 12 are provided to detect the inlet and outlet side oxygen temperatures of the liquid oxygen pump 2, respectively. The temperature detectors 11 and 12 may be implemented as, for example, thermistors, which have a characteristic of changing a resistance value according to temperature change.

In the above configuration, the precooling completion determination unit 30 and the resistance / voltage converter 31 for converting a resistance value corresponding to the temperature detected by the inlet and outlet temperature detectors 12, 11 and a voltage signal; A subtractor 32 receiving a temperature detection signal converted into a voltage signal by the resistor / voltage converter 31 and calculating a difference between the two temperature detection values, a pump inlet calculated by the subtractor 32, For example, a predetermined temperature for determining whether the temperature difference between the outlets is a predetermined temperature for determining whether the precooling is completed is -2 ° C. or less, and a preset time period when the temperature difference between the comparator 33 and the comparator 33 is -2 ° C. or less. It is provided with a timer 34 that determines whether the lasting 10 seconds or more. At this time, if it is determined by the timer 34 that the time difference between the inlet / outlet side temperature of the liquid oxygen pump 2 is -2 ° C. or less is maintained for 10 seconds or more, it is determined that the precooling is completed, and the timer 34 determines that the pump driving unit 40 A high level operation signal is output to the OR gate 41.

On the other hand, the pump start unit 40 inputs a start switch 13 which is turned on according to the driver's operation, a pump precooling signal input by the operation of the start switch 13 and a precooling completion signal from the precooling completion determination unit 30. An AND gate 42 for performing an AND operation on the output signal of the OR gate 41, a transistor operated by receiving the output signal of the AND gate 42 as a base driving signal, and a And a relay RY connected to the collector stage and outputting a drive signal to the liquid oxygen pump driving motor 3.

3 is a circuit diagram showing a detailed configuration of an automatic precooling control unit according to the present invention. As shown in FIG. 3, the automatic precooling control unit 50 according to the present invention receives an output resistance value of the outlet temperature detector 11 whose resistance value changes according to the outlet temperature change of the liquid oxygen pump 2. The resistance / voltage converter 51 converts and outputs a voltage signal corresponding to the corresponding temperature and outputs the pump outlet side temperature detected by the outlet temperature detector 11 when the start switch 13 is turned on. 51 is provided with a plurality of comparators (52a ~ 52e) received as a work input signal through the plurality of comparators 52, each of the plurality of comparators 52 is set a reference temperature for controlling the opening amount of the outlet valve step by step have. For example, the first comparator 52a is 20 ° C as the reference temperature, the second comparator 52b is -30 ° C, the third comparator 52c is -105 ° C, the fourth comparator 52d is -155 ° C, and 5 comparator 52e is set to -182 ° C.

Accordingly, each comparator 52 outputs a high level signal for each temperature as the pump outlet temperature changes, thereby driving the transistor TR connected to the output terminal of each comparator 52. At this time, in order to control the opening amount of the pump inlet valve 4 and the pump outlet valve 5, the opening amount according to the pump outlet side temperature is set in the collector terminal of each transistor. The higher the pump outlet valve side temperature is, the smaller the opening amount is, and the lower the pump outlet valve side temperature is, the closer to the precooling completion point, the value of each variable resistor is set to increase the valve opening amount. The output voltage signal of each transistor TR according to the resistance of the variable resistor is input to the voltage / current converter 54 through the high signal automatic selector 53 and converted into a current signal, and then the pump inlet valve 4 and the pump. Output to the outlet valve (5).

The change in the valve opening amount according to the pump outlet side temperature according to the control of the automatic precooling control unit 50 is the same as the graph shown in FIG. That is, as the temperature of the pump outlet side decreases, the opening amount of the valve is increased little by little so that the cryogenic liquid oxygen does not rapidly enter the liquid oxygen pump 2. In addition, Figure 4 (b) is a graph showing the temperature change of the pump according to the pre-cooling time.

5 is a circuit diagram showing a detailed configuration of an automatic boosting controller according to the present invention. As shown in FIG. 5, the automatic boosting controller 60 according to the present invention starts to drive the liquid oxygen pump 2 and pumps liquid oxygen from the liquid oxygen tank 1 to supply it to the evaporator side. By outputting a proper control signal to the pressure adjusting unit 20 to gradually increase the pressure of the liquid oxygen supplied to the evaporator side to a predetermined reference pressure, for example 25kg / ㎠ step by step to maintain a constant.

When the start switch 13 is turned on and the pump is driven, the automatic booster control unit 60 receives the ON signal of the start switch 13 to operate the timer 61 to count time in a predetermined time unit, for example, in seconds. do. The time counted by the timer 61 is output as one input signal of the plurality of comparators 66 in which the reference time is set differently. At this time, each of the comparators 66a to 66e compares the preset reference time with the signal output from the timer 61 to operate when the count time becomes more than the reference time, thereby outputting a high level signal. In addition, transistors TR1 to TR5, the operation of which is turned on or off according to the output signal of the comparator 66, are provided at the output terminal of each comparator 66, and different liquids are provided at the collector terminals of the transistors TR1 to TR5. When the oxygen pressure value is set and any one of the transistors is turned on, the liquid oxygen pressure value set at the collector end of the transistor is selectively output through the high signal automatic selector 67. In this case, the output liquid oxygen pressure value is converted into a current signal through the voltage / current converter 68 and then input as a reference set value of the discharge pressure adjusting unit 20.

Hereinafter, the operation of the automatic precooling control device for the liquid oxygen pump according to the present invention having such a configuration will be described.

First, when the operator determines that there is a reason to operate the liquid oxygen pump 2 and turns on the start switch 13, the pump inlet valve 4 and the pump outlet valve 5 are opened a small amount to open the liquid oxygen tank 1. Is supplied to the liquid oxygen pump (2). In this case, a precooling operation of the liquid oxygen pump 2 is performed. At this time, the temperature signal measured by the pump outlet temperature detector 11 is input to the pump automatic precooling control unit 50.

The automatic precooling control unit 50 receives the temperature signal detected from the pump outlet temperature detector 11 and compares the signals through the respective comparators 52. In the non-inverting terminals of each of the comparators 52a to 52e, reference temperatures for controlling the opening amounts of the pump inlet and outlet valves for each temperature are set. Therefore, when the temperature signal detected by the pump outlet temperature detector 11 is input to the inverting terminals of the comparators 52a to 52e and compared with the reference temperature set in the non-inverting terminal, the detected temperature is lower than the reference temperature. Outputs a high level signal to the output side.

That is, the first comparator 52a outputs a high signal and turns on the transistor TRa when the pump outlet side temperature is lower than 20 ° C., the reference temperature, so that the control signal corresponding to the opening amount 10% set in the transistor TRa is turned on. Is output to the pump inlet valve (3) and the pump outlet valve (4) via the high signal autoselector (53). On the other hand, the second comparator TRb turns on the transistor TRb so that the opening degree of the pump inlet / outlet valve is opened by 20% by outputting a high level signal when the detected detection temperature is lower than the reference temperature of -30 ° C. .

Meanwhile, when the liquid oxygen pump outlet temperature becomes −105 ° C. or less as the precooling of the liquid oxygen pump 2 proceeds, the output of the third comparator TRc becomes high (logical '1') and the liquid oxygen pump 2 When the outlet temperature is below -155 ° C, the output of the fourth comparator TRd also becomes high. When the liquid oxygen pump outlet temperature is lower than −183 ° C., the fifth comparator TRe output is also high, and the entire comparator output maintains a high signal. Accordingly, as the liquid oxygen pump outlet side temperature gradually decreases due to the precooling of the liquid oxygen pump, the pump inlet valve 3 and the pump outlet valve according to the valve opening amount set in the transistor TR connected to the output terminal of each comparator 52. The opening amount in (4) is to be controlled.

When the output of at least one of the first comparators 52a to the fifth comparator 52e becomes high, the transistor connected to the output terminal is turned off to output a high signal to the high signal automatic selector 53. At this time, the high signal automatic selector 53 selects the largest signal among the input signals and outputs it to the valve.

By this method, the pump continues precooling, and when the pump outlet temperature is -183 ° C. or lower, the liquid oxygen pump inlet valve 3 and the pump outlet valve 4 are kept 100% open.

Figure 4 (a) is a graph showing the valve operation signal in accordance with the liquid oxygen pump outlet temperature change, it can be seen that the opening degree of the valve gradually opened, and the opening degree of the valve is controlled to increase as the temperature of the pump outlet side drops. In addition, when performing the liquid oxygen pump precooling process, the liquid oxygen passing through the pump outlet valve 4 is returned to the liquid oxygen tank 1 and reused without being thrown into the atmosphere as conventionally.

Figure 4 (b) shows the liquid oxygen pump precooling temperature trend, it takes about 30 minutes to start and complete the pre-cooling of the liquid oxygen pump, it shows that the liquid oxygen pump outlet temperature is slowly falling normally during the precooling . When the precooling of the liquid oxygen pump is completed, the liquid oxygen pump inlet valve 3 and the pump outlet valve 4 are automatically opened 100% to prepare for starting the liquid oxygen pump.

When the temperature at the pump outlet side drops below -183 ° C by this precooling operation, the precooling completion determination unit 30 compares the pump inlet temperature with the pump outlet temperature and calculates the temperature difference at the subtractor 32, and the calculated temperature difference is-. When it is 2 degrees C or less, ie, when it is determined that the pump outlet side temperature is -183 degrees C or less, the timer 34 is driven. The timer 34 determines that the time when the temperature difference between the pump inlet / outlet side is within −2 ° C. has elapsed for a predetermined time, that is, 10 seconds or more, and outputs a pump start signal to the pump start unit 40 to operate the liquid oxygen pump 2. Will be activated.

When the liquid oxygen pump 2 is started, in order to protect the liquid oxygen pump 2, the discharge flow rate is first returned to the entire tank 1, and then the liquid oxygen pump discharge pressure is gradually raised by the automatic boosting controller 60. To perform the control.

That is, when the liquid oxygen pump precooling is completed and the liquid oxygen pump starting relay RY is operated, this signal is input to the automatic boosting controller 60 for stepping up the pump discharge pressure to operate the timer 61. . From this time, the timer 61 counts time in seconds, and the counted time is input as one input signal of each comparator 66 of the time comparator.

In the type force stages of the first and fifth comparators 66a and 66e, respectively, 10 seconds, 30 seconds, 50 seconds, 70 seconds, and 90 seconds are set as time intervals for boosting the pressure of the liquid oxygen, respectively. Accordingly, each comparator 66 compares the time counted by the timer 61 with a preset reference time and outputs a high or low signal according to the comparison result. In other words, the first comparator 66a outputs a high signal when the time counted by the timer 61 is 10 seconds or more, and the second comparator 66b outputs a high signal when it is 30 seconds or more.

In addition, a variable resistor for controlling the discharge pressure of liquid oxygen is provided at the collector terminals of the transistors TR1 to TR5 connected to the output terminals of the comparators 66, respectively, depending on the resistance set value of each variable resistor, 10 [kg / cm 2]. , 16 [kg / cm 2], 20 [kg / cm 2], 23 [kg / cm 2], and 25 [kg / cm 2] are outputted to the high signal automatic selector 67.

FIG. 6 is a graph showing a pump discharge pressure control state according to the present invention. When the time counted by the timer 61 of the automatic boosting controller 60 is 10 seconds or more, the first comparator 66a is a high signal. The transistor TR1 is operated to output a discharge pressure signal of 10 [kg / cm 2] to the discharge pressure control unit 20 as a set value. Accordingly, the discharge pressure control unit 20 compares the set value received from the automatic boosting control unit 60 with the pressure detected through the discharge pressure detector 8 to open the discharge pressure regulating valve 9 so as to compensate for the difference. The quantity is adjusted so that the discharge pressure of the liquid oxygen can be maintained at the set value. In addition, when the time counted by the timer 61 is 30 seconds or more, the second comparator 66b outputs a high signal to operate the transistor TR2, and accordingly, the discharge pressure control unit 20 supplies 16 [kg / cm 2]. ] Is entered as the set value.

On the other hand, the automatic boosting control unit 60 automatically raises the set value of the discharge pressure control unit 20 according to time, and when the pressure rises due to abnormal process or disturbance or excessively rises, the timer 61 is turned on. Temporarily stops to maintain the holding state. It detects the control pressure value output to the discharge pressure control unit 20 through the high signal automatic selector 67, and the difference between the detected control pressure value and the pressure value detected through the discharge pressure detector 8 is 1 [. kg / cm 2] or less, the lower limit comparator 62 outputs a high signal and outputs a timer hold signal. In addition, when the discharge pressure detected through the discharge pressure detector 8 is 25 [kg / cm 2] or more set to an appropriate discharge pressure, the output signal of the upper limit comparator 63 becomes high and is output as a timer hold signal.

After the pump discharge pressure rises to normal, since the pump discharge pressure adjusting unit 20 is always set to 25 [kg / cm 2], the discharge pressure regulating valve 9 is compared with the measured pressure measured by the pump discharge pressure detector 8. Will be controlled. 5 is a pump discharge pressure boost control state graph, it can be seen that the pressure is gradually increased as the pressure is increased and the pressure is gradually increased in a low pressure state.

On the other hand, Figure 7 is a test graph when determining the boosting time for implementing the present invention, in order to determine the unit time for boosting the discharge pressure in one embodiment of the present invention 2.5 [kg / ㎠] discharge pressure every 10 seconds The automatic boosting control unit 60 was configured to boost the pressure. As shown in FIG. 6, when the discharge pressure is boosted by 2.5 [kg / cm 2] every 3 seconds (top graph), when the discharge pressure is boosted by 2.5 [kg / cm 2] every 15 seconds (top The vibration of the liquid oxygen pump was tested for each of the following graphs) and the case of raising the discharge pressure by 2.5 [kg / cm 2] every 10 seconds (middle graph).

Considering the test result shows that the pump's vibration risk value is 1.0 [mill] and the threshold value is 0.7 [mill], the vibration does not exceed the threshold value even when the discharge pressure is 25 [kg / cm 2] when the unit time is 15 seconds. However, there is a problem that it takes a long time to increase the pressure up to the set discharge pressure as the unit time is set longer. In addition, when the unit time was shortened to 3 seconds, there was a problem in that the vibration of the pump exceeded a dangerous value when the pressure was increased to 25 [kg / cm 2], which is the set discharge pressure. On the other hand, when the unit time is set to 10 seconds, it can be seen that the pressure can be increased in a short time up to the set discharge pressure, and even if the pressure is completed, it does not affect the pump vibration.

The automatic precooling control device for the liquid oxygen pump according to the present invention is not limited to the above-described embodiments, and may be variously modified and implemented within the range permitted by the technical idea of the present invention.

As described above, the automatic precooling control device for the liquid oxygen pump according to the present invention automatically precools the liquid oxygen pump when driving the liquid oxygen pump to pump the liquid oxygen from the liquid oxygen tank and supplying the oxygen to the oxygen use plant. Step by step, the discharge pressure of the liquid oxygen is raised to discharge. Therefore, it is possible to prevent mechanical damage and loss of money due to the introduction of cryogenic liquid oxygen into the pump during precooling of the liquid oxygen pump, and to prevent waste of liquid oxygen during the precooling operation.

In addition, by sequentially boosting the discharge pressure of the liquid oxygen discharged from the liquid oxygen pump when the pre-cooling is completed, it is possible to prevent damage to the pump bearing and sealing device for preventing leakage caused by the sudden increase in the discharge pressure of the liquid oxygen pump Can be obtained.

Claims (5)

In the drive control device of the liquid oxygen pump for supplying the excess liquid oxygen stored in the liquid oxygen tank with an emergency pump and then supplied to the oxygen using process, A pump inlet / outlet valve provided at an inlet and an outlet of the oxygen pump to control a flow rate flowing from the liquid oxygen tank and a discharge rate from the pump; An automatic precooling control unit for controlling the opening amount of the pump inlet / outlet valves so that when the driving start signal of the liquid oxygen pump is input, liquid oxygen is sequentially supplied to the liquid oxygen pump to precool the liquid oxygen pump; A temperature detector each provided to detect inlet and outlet temperature of the liquid oxygen pump; A precooling completion determination unit determining whether the precooling is completed according to the temperature difference calculated by receiving the pump inlet and outlet temperature detected by the temperature detector; And a pump starting unit for starting the liquid oxygen pump to pump and discharge the liquid oxygen when it is determined that the precooling is completed. The method of claim 1, wherein the automatic precooling control unit A plurality of comparators for receiving a temperature signal detected by the pump outlet temperature detector at one input terminal and comparing the temperature signal set at a type force terminal to a reference temperature differently; A plurality of transistors connected to each output terminal of the comparator and operated when the comparison result detection signal of the comparator is lower than the reference temperature to output a corresponding valve opening amount value according to the temperature decrease of the pump outlet side; And a high signal automatic selector which selects the largest value of the valve openings output from the transistors and outputs them to the pump inlet / outlet valves. The method of claim 1, wherein the precooling completion determination unit A subtractor for receiving a temperature signal detected by the pump inlet / outlet temperature detector and calculating a temperature difference; A comparator for comparing the pump inlet / outlet temperature difference calculated by the subtractor with a preset reference temperature for precooling completion determination; And a timer for outputting a precooling completion signal to the pump starter after the preset reference time has elapsed when the pump inlet / outlet temperature difference is less than the reference temperature as a result of the comparison of the comparator. Automatic precooling control device. The method of claim 1, A discharge pressure detector for detecting a discharge pressure of the liquid oxygen output according to the start of the liquid oxygen pump; An automatic boosting controller for outputting a predetermined pressure setting signal to step up the discharge pressure of the liquid oxygen in a predetermined time unit to a predetermined supply pressure when the pump is started; A discharge pressure adjusting unit for comparing the discharge pressure detected by the discharge pressure detector with a set pressure output from the automatic boosting controller and outputting a control signal for compensating for the difference; And a discharge pressure regulating valve for adjusting a pressure of the liquid oxygen output from the liquid oxygen pump in accordance with a control signal output from the discharge pressure adjusting unit. The method of claim 4, wherein the automatic boosting control unit A timer for counting and outputting a pump driving time by starting a time count when a pump driving start signal is input; A plurality of comparators for receiving a time counted by the timer as a work input signal and comparing the time counted with each other; A plurality of transistors connected to each output terminal of the comparator and operated when the pump driving time is equal to or greater than each reference time to output discharge pressure set values for each pump driving time; And a high signal automatic selector configured to select the largest value among the discharge pressure set values output from the transistors and to output the set pressure value of the pump discharge pressure adjusting unit.